<!DOCTYPE HTML>
<html lang="zh-CN">


<head>
    <meta charset="utf-8">
    <meta name="keywords" content="函数式编程简介, Java，Flutter，Dart，架构，编程，技术分享，读书分享">
    <meta name="description" content="函数式编程是什么函数式编程是一种编程范式，大部分人已知的编程范式有C的命令式，Java的面向对象，我们不需要从学术的角度，来严格定义函数式编程，并且函数式和面向对象也不是非此即彼的关系，强大如Scala也是混合式范式语言，我们从实用角度来介">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
    <meta name="renderer" content="webkit|ie-stand|ie-comp">
    <meta name="mobile-web-app-capable" content="yes">
    <meta name="format-detection" content="telephone=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
    <meta name="referrer" content="no-referrer-when-downgrade">
    <!-- Global site tag (gtag.js) - Google Analytics -->


    <title>函数式编程简介 | 武码公社</title>
    <link rel="icon" type="image/png" href="/favicon.png">

    <link rel="stylesheet" type="text/css" href="/libs/awesome/css/all.css">
    <link rel="stylesheet" type="text/css" href="/libs/materialize/materialize.min.css">
    <link rel="stylesheet" type="text/css" href="/libs/aos/aos.css">
    <link rel="stylesheet" type="text/css" href="/libs/animate/animate.min.css">
    <link rel="stylesheet" type="text/css" href="/libs/lightGallery/css/lightgallery.min.css">
    <link rel="stylesheet" type="text/css" href="/css/matery.css">
    <link rel="stylesheet" type="text/css" href="/css/my.css">

    <script src="/libs/jquery/jquery.min.js"></script>

<meta name="generator" content="Hexo 5.4.0"></head>




<body>
    <header class="navbar-fixed">
    <nav id="headNav" class="bg-color nav-transparent">
        <div id="navContainer" class="nav-wrapper container">
            <div class="brand-logo">
                <a href="/" class="waves-effect waves-light">
                    
                    <img src="/medias/logo.png" class="logo-img" alt="LOGO">
                    
                    <span class="logo-span">武码公社</span>
                </a>
            </div>
            

<a href="#" data-target="mobile-nav" class="sidenav-trigger button-collapse"><i class="fas fa-bars"></i></a>
<ul class="right nav-menu">
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/" class="waves-effect waves-light">
      
      <i class="fas fa-home" style="zoom: 0.6;"></i>
      
      <span>首页</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/tags" class="waves-effect waves-light">
      
      <i class="fas fa-tags" style="zoom: 0.6;"></i>
      
      <span>标签</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/categories" class="waves-effect waves-light">
      
      <i class="fas fa-bookmark" style="zoom: 0.6;"></i>
      
      <span>分类</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/archives" class="waves-effect waves-light">
      
      <i class="fas fa-archive" style="zoom: 0.6;"></i>
      
      <span>归档</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/about" class="waves-effect waves-light">
      
      <i class="fas fa-user-circle" style="zoom: 0.6;"></i>
      
      <span>关于</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/contact" class="waves-effect waves-light">
      
      <i class="fas fa-comments" style="zoom: 0.6;"></i>
      
      <span>留言板</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a target="_blank" rel="noopener" href="https://lox.dengwu.wang" class="waves-effect waves-light">
      
      <i class="fas fa-book" style="zoom: 0.6;"></i>
      
      <span>自己动手写解释器</span>
    </a>
    
  </li>
  
  <li>
    <a href="#searchModal" class="modal-trigger waves-effect waves-light">
      <i id="searchIcon" class="fas fa-search" title="搜索" style="zoom: 0.85;"></i>
    </a>
  </li>
</ul>


<div id="mobile-nav" class="side-nav sidenav">

    <div class="mobile-head bg-color">
        
        <img src="/medias/logo.png" class="logo-img circle responsive-img">
        
        <div class="logo-name">武码公社</div>
        <div class="logo-desc">
            
            思考和积累
            
        </div>
    </div>

    <ul class="menu-list mobile-menu-list">
        
        <li class="m-nav-item">
	  
		<a href="/" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-home"></i>
			
			首页
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/tags" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-tags"></i>
			
			标签
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/categories" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-bookmark"></i>
			
			分类
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/archives" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-archive"></i>
			
			归档
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/about" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-user-circle"></i>
			
			关于
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/contact" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-comments"></i>
			
			留言板
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a target="_blank" rel="noopener" href="https://lox.dengwu.wang" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-book"></i>
			
			自己动手写解释器
		</a>
          
        </li>
        
        
        <li><div class="divider"></div></li>
        <li>
            <a href="https://github.com/wangdengwu" class="waves-effect waves-light" target="_blank">
                <i class="fab fa-github-square fa-fw"></i>我的代码库
            </a>
        </li>
        
    </ul>
</div>


        </div>

        
            <style>
    .nav-transparent .github-corner {
        display: none !important;
    }

    .github-corner {
        position: absolute;
        z-index: 10;
        top: 0;
        right: 0;
        border: 0;
        transform: scale(1.1);
    }

    .github-corner svg {
        color: #0f9d58;
        fill: #fff;
        height: 64px;
        width: 64px;
    }

    .github-corner:hover .octo-arm {
        animation: a 0.56s ease-in-out;
    }

    .github-corner .octo-arm {
        animation: none;
    }

    @keyframes a {
        0%,
        to {
            transform: rotate(0);
        }
        20%,
        60% {
            transform: rotate(-25deg);
        }
        40%,
        80% {
            transform: rotate(10deg);
        }
    }
</style>

<a href="https://github.com/wangdengwu" class="github-corner tooltipped hide-on-med-and-down" target="_blank"
   data-tooltip="我的代码库" data-position="left" data-delay="50">
    <svg viewBox="0 0 250 250" aria-hidden="true">
        <path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path>
        <path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2"
              fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path>
        <path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z"
              fill="currentColor" class="octo-body"></path>
    </svg>
</a>
        
    </nav>

</header>

    



<div class="bg-cover pd-header post-cover" style="background-image: url('/medias/featureimages/12.jpg')">
    <div class="container" style="right: 0px;left: 0px;">
        <div class="row">
            <div class="col s12 m12 l12">
                <div class="brand">
                    <h1 class="description center-align post-title">函数式编程简介</h1>
                </div>
            </div>
        </div>
    </div>
</div>




<main class="post-container content">

    
    <link rel="stylesheet" href="/libs/tocbot/tocbot.css">
<style>
    #articleContent h1::before,
    #articleContent h2::before,
    #articleContent h3::before,
    #articleContent h4::before,
    #articleContent h5::before,
    #articleContent h6::before {
        display: block;
        content: " ";
        height: 100px;
        margin-top: -100px;
        visibility: hidden;
    }

    #articleContent :focus {
        outline: none;
    }

    .toc-fixed {
        position: fixed;
        top: 64px;
    }

    .toc-widget {
        width: 345px;
        padding-left: 20px;
    }

    .toc-widget .toc-title {
        padding: 35px 0 15px 17px;
        font-size: 1.5rem;
        font-weight: bold;
        line-height: 1.5rem;
    }

    .toc-widget ol {
        padding: 0;
        list-style: none;
    }

    #toc-content {
        padding-bottom: 30px;
        overflow: auto;
    }

    #toc-content ol {
        padding-left: 10px;
    }

    #toc-content ol li {
        padding-left: 10px;
    }

    #toc-content .toc-link:hover {
        color: #42b983;
        font-weight: 700;
        text-decoration: underline;
    }

    #toc-content .toc-link::before {
        background-color: transparent;
        max-height: 25px;

        position: absolute;
        right: 23.5vw;
        display: block;
    }

    #toc-content .is-active-link {
        color: #42b983;
    }

    #floating-toc-btn {
        position: fixed;
        right: 15px;
        bottom: 76px;
        padding-top: 15px;
        margin-bottom: 0;
        z-index: 998;
    }

    #floating-toc-btn .btn-floating {
        width: 48px;
        height: 48px;
    }

    #floating-toc-btn .btn-floating i {
        line-height: 48px;
        font-size: 1.4rem;
    }
</style>
<div class="row">
    <div id="main-content" class="col s12 m12 l9">
        <!-- 文章内容详情 -->
<div id="artDetail">
    <div class="card">
        <div class="card-content article-info">
            <div class="row tag-cate">
                <div class="col s7">
                    
                    <div class="article-tag">
                        
                            <a href="/tags/%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BC%96%E7%A8%8B/">
                                <span class="chip bg-color">函数式编程</span>
                            </a>
                        
                    </div>
                    
                </div>
                <div class="col s5 right-align">
                    
                    <div class="post-cate">
                        <i class="fas fa-bookmark fa-fw icon-category"></i>
                        
                            <a href="/categories/%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BC%96%E7%A8%8B/" class="post-category">
                                函数式编程
                            </a>
                        
                    </div>
                    
                </div>
            </div>

            <div class="post-info">
                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-minus fa-fw"></i>发布日期:&nbsp;&nbsp;
                    2021-11-24
                </div>
                

                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-check fa-fw"></i>更新日期:&nbsp;&nbsp;
                    2022-02-18
                </div>
                

                
                <div class="info-break-policy">
                    <i class="far fa-file-word fa-fw"></i>文章字数:&nbsp;&nbsp;
                    2.4k
                </div>
                

                

                
            </div>
        </div>
        <hr class="clearfix">

        
        <!-- 是否加载使用自带的 prismjs. -->
        <link rel="stylesheet" href="/libs/prism/prism.css">
        

        

        <div class="card-content article-card-content">
            <div id="articleContent">
                <h3 id="函数式编程是什么"><a href="#函数式编程是什么" class="headerlink" title="函数式编程是什么"></a>函数式编程是什么</h3><p>函数式编程是一种编程范式，大部分人已知的编程范式有C的命令式，Java的面向对象，我们不需要从学术的角度，来严格定义函数式编程，并且函数式和面向对象也不是非此即彼的关系，强大如Scala也是混合式范式语言，我们从实用角度来介绍和解读函数式编程。<br>函数式编程至少应该具有以下特性：</p>
<ul>
<li>函数是一等公民</li>
<li>支持匿名函数</li>
<li>闭包</li>
<li>柯里化</li>
<li>惰性求值</li>
<li>参数多态</li>
<li>代数数据类型</li>
<li>。。。</li>
</ul>
<p>函数式编程理所当然是以函数为主要编程对象，而面向对象则以对象为主要编程对象，但是你仔细想想，面向对象如果没有方法，而只是有一堆属性的类，哪还有什么功能价值呢？所以即便是面向对象也离不开方法，当然这里的方法除了不是一等公民以外，和函数式编程差别也很大，那差别在哪里了？</p>
<h3 id="纯函数"><a href="#纯函数" class="headerlink" title="纯函数"></a>纯函数</h3><p>纯函数，又称为没有副作用，或者引用透明，那什么样的方法是没有副作用的呢？</p>
<ul>
<li>方法的参数值不变，则返回值就不会改变，比如random函数就不是纯函数。</li>
<li>必须有返回值。</li>
<li>方法不会对外界变量造成改变，即便是打印日志，控制台输出，都不可以。</li>
<li>不能抛出异常，即便是抛出异常也不是纯函数。</li>
</ul>
<p>纯函数有什么好处呢？</p>
<ul>
<li>独立性，因为不会依赖外部变量，只依赖输入的参数，很方便进行单元测试。</li>
<li>确定性，相同的参数，总是返回相同的结果，不会出现诡异的bug。</li>
<li>安全性，不用担心它抛出异常，函数调用等价于表达式。</li>
<li>结合高阶函数，稳定的纯函数复合出来的函数依然具备以上特性。</li>
</ul>
<h3 id="手写纯函数"><a href="#手写纯函数" class="headerlink" title="手写纯函数"></a>手写纯函数</h3><p>我们下面使用Java来写一个纯函数，虽然Java它并不是函数式的语言，但是并不妨碍我们展示函数式编程，有些语言对函数式编程比较友好，比如Scala，但是函数式编程并不仅仅取决于语言，而是取决于你怎么写代码。<br>自从Java8开始支持lambda表达式开始，Java已经有点函数式的味道了。我们先从一个接口开始，因为Java里函数不是一等公民，所以我们只能从接口定义函数。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">,</span> <span class="token class-name">U</span><span class="token punctuation">></span></span> <span class="token punctuation">&#123;</span>
    <span class="token class-name">U</span> <span class="token function">apply</span><span class="token punctuation">(</span><span class="token class-name">T</span> arg<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<p>我们来做一下单元测试</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">FunctionTest</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> add <span class="token operator">=</span> x <span class="token operator">-></span> x <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> multi <span class="token operator">=</span> x <span class="token operator">-></span> x <span class="token operator">*</span> <span class="token number">2</span><span class="token punctuation">;</span>
    
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testApply</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> add<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> multi<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>add和multi就是纯函数。这个apply的定义虽然看起来很基础简单，但是就像函数式的基石一样，非常有用。</p>
<h3 id="高阶函数"><a href="#高阶函数" class="headerlink" title="高阶函数"></a>高阶函数</h3><p>什么是高阶函数呢？别被高阶给吓到，其实就是可以接收函数作为参数，并且可以返回函数的函数。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">,</span> <span class="token class-name">U</span><span class="token punctuation">></span></span> <span class="token punctuation">&#123;</span>
    <span class="token class-name">U</span> <span class="token function">apply</span><span class="token punctuation">(</span><span class="token class-name">T</span> arg<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">default</span> <span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">></span></span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">,</span> <span class="token class-name">U</span><span class="token punctuation">></span></span> <span class="token function">compose</span><span class="token punctuation">(</span><span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">,</span> <span class="token class-name">T</span><span class="token punctuation">></span></span> f<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">return</span> v <span class="token operator">-></span> <span class="token function">apply</span><span class="token punctuation">(</span>f<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>来看单元测试</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">FunctionTest</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> add <span class="token operator">=</span> x <span class="token operator">-></span> x <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> multi <span class="token operator">=</span> x <span class="token operator">-></span> x <span class="token operator">*</span> <span class="token number">2</span><span class="token punctuation">;</span>

    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testApply</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> add<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> multi<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testCompose</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> compose <span class="token operator">=</span> add<span class="token punctuation">.</span><span class="token function">compose</span><span class="token punctuation">(</span>multi<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Integer</span> result <span class="token operator">=</span> compose<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> result<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>add组合函数multi生成了新的函数compose，调用该函数得到返回值，其实就是执行了1+1*2 = 3<br>对函数式编程有点感觉了吗？这才只是开胃菜，让我们继续烧脑。</p>
<h3 id="柯里化"><a href="#柯里化" class="headerlink" title="柯里化"></a>柯里化</h3><p>函数是可以有多个参数的，以2个参数的举例，f(x,y) = x+y*2 有时候我们并不想一次性把2个参数都确定，而只是固定一个参数，以固定的这个参数为函数，再应用另外一个参数，比如我们先固定x=1,然后再应用这个得到的函数y=2，y=3，就可以得到一个对参数加倍再固定+1的函数。<br>但是，我们之前定义的apply方法只有一个参数怎么办？其实把函数看成只有一个参数，引入Tuple类型，先看下Tuple的定义</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Tuple</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">,</span> <span class="token class-name">U</span><span class="token punctuation">></span></span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token class-name">T</span> _1<span class="token punctuation">;</span>
    <span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token class-name">U</span> _2<span class="token punctuation">;</span>

    <span class="token keyword">public</span> <span class="token class-name">Tuple</span><span class="token punctuation">(</span><span class="token class-name">T</span> t<span class="token punctuation">,</span> <span class="token class-name">U</span> u<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>_1 <span class="token operator">=</span> t<span class="token punctuation">;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>_2 <span class="token operator">=</span> u<span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>很简单，就是参数的盒子而已，这样我们就可以使用之前定义的函数来传入2个参数了。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">static</span> <span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">A</span><span class="token punctuation">,</span> <span class="token class-name">B</span><span class="token punctuation">,</span> <span class="token class-name">C</span><span class="token punctuation">></span></span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">A</span><span class="token punctuation">,</span> <span class="token class-name">Function</span><span class="token punctuation">&lt;</span><span class="token class-name">B</span><span class="token punctuation">,</span> <span class="token class-name">C</span><span class="token punctuation">></span><span class="token punctuation">></span></span> <span class="token function">curry</span><span class="token punctuation">(</span><span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Tuple</span><span class="token punctuation">&lt;</span><span class="token class-name">A</span><span class="token punctuation">,</span> <span class="token class-name">B</span><span class="token punctuation">></span><span class="token punctuation">,</span> <span class="token class-name">C</span><span class="token punctuation">></span></span> f<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
       <span class="token keyword">return</span> a <span class="token operator">-></span> b <span class="token operator">-></span> f<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Tuple</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">></span></span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> b<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>
<p>单元测试如下</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Function</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Tuple</span><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span> addWithTuple <span class="token operator">=</span> t <span class="token operator">-></span> t<span class="token punctuation">.</span>_1 <span class="token operator">+</span> t<span class="token punctuation">.</span>_2 <span class="token operator">*</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testCurry</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token class-name">Integer</span> result <span class="token operator">=</span> <span class="token class-name">Function</span><span class="token punctuation">.</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">></span></span><span class="token function">curry</span><span class="token punctuation">(</span>addWithTuple<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">assertEquals</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span> result<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<h3 id="惰性求值"><a href="#惰性求值" class="headerlink" title="惰性求值"></a>惰性求值</h3><p>惰性求值是指只有在真正获取的时候，才去执行函数，举个栗子</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testLazy</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token function">add</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token function">recursion</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span>

<span class="token keyword">private</span> <span class="token class-name">Integer</span> <span class="token function">recursion</span><span class="token punctuation">(</span><span class="token class-name">Integer</span> b<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">return</span> <span class="token function">recursion</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span>

<span class="token keyword">private</span> <span class="token class-name">Integer</span> <span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">int</span> a<span class="token punctuation">,</span> <span class="token keyword">int</span> b<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">return</span> a<span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>执行上面的代码，就会得到java.lang.StackOverflowError，我们明明不需要b的结果，但是由于Java表达式并不支持惰性，所以导致递归函数一直执行到爆栈。<br>我们来改造一下。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">testLazy</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token function">add</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token function">recursion</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span>

<span class="token keyword">private</span> <span class="token class-name">Integer</span> <span class="token function">recursion</span><span class="token punctuation">(</span><span class="token class-name">Integer</span> b<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">return</span> <span class="token function">recursion</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span>

<span class="token keyword">private</span> <span class="token class-name">Integer</span> <span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">int</span> a<span class="token punctuation">,</span> <span class="token class-name">Supplier</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> b<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">return</span> a<span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>好吧，我承认我作弊，改变了参数类型，但是这个例子只是让你感觉一下，什么是惰性求值。</p>
<h3 id="模式匹配"><a href="#模式匹配" class="headerlink" title="模式匹配"></a>模式匹配</h3><p>函数式最有用的一个功能，我觉得就是模式匹配，因为可以很好的消除if else，命令式往往充斥着if else，而这些往往是令人难以理解和产生bug的地方，因此难于维护，而函数式编程里，只有表达式没有语句，if else往往纠结在细节里，而函数式编程通过代数数据类型，以及解构对象来对表达式进行匹配，可以很优雅的解决if else的问题。下面我们来演示一下如何消除if else，这次因为Java表达能力不够简洁，我们使用kotlin来做演示</p>
<h4 id="需求"><a href="#需求" class="headerlink" title="需求"></a>需求</h4><ul>
<li>计算个人所得税</li>
<li>如果一个人有房子则减免100再计税</li>
<li>如果一个人有孩子则减免200再计税</li>
<li>减免后大于等于1000则缴税减免后金额的3%</li>
<li>减免后大于等于3000则缴税减免后金额的5%</li>
<li>求应交税多少，不考虑精度丢失等情况</li>
</ul>
<p>过程式函数实现</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/**
 * 计算个人所得税
 * 如果一个人有房子则减免100再计税
 * 如果一个人有孩子则减免200再计税
 * 减免后大于等于1000则缴税减免后金额的3%
 * 减免后大于等于3000则缴税减免后金额的5%
 * 求应交税多少，不考虑精度丢失等情况
 */</span>
 <span class="token keyword">private</span> <span class="token keyword">double</span> <span class="token function">tax</span><span class="token punctuation">(</span><span class="token keyword">boolean</span> hasHouse<span class="token punctuation">,</span> <span class="token keyword">boolean</span> hasChild<span class="token punctuation">,</span> <span class="token keyword">double</span> money<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">double</span> firstLevel <span class="token operator">=</span> <span class="token number">1000</span><span class="token punctuation">;</span>
        <span class="token keyword">double</span> firstLevelReduce <span class="token operator">=</span> <span class="token number">100</span><span class="token punctuation">;</span>
        <span class="token keyword">double</span> secondLevel <span class="token operator">=</span> <span class="token number">3000</span><span class="token punctuation">;</span>
        <span class="token keyword">double</span> secondLevelReduce <span class="token operator">=</span> <span class="token number">200</span><span class="token punctuation">;</span>
        <span class="token keyword">double</span> tax <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
        <span class="token keyword">double</span> after <span class="token operator">=</span> money<span class="token punctuation">;</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>hasHouse<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>hasChild<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                after <span class="token operator">=</span> money <span class="token operator">-</span> secondLevelReduce <span class="token operator">-</span> firstLevelReduce<span class="token punctuation">;</span>
            <span class="token punctuation">&#125;</span> <span class="token keyword">else</span> <span class="token punctuation">&#123;</span>
                after <span class="token operator">=</span> money <span class="token operator">-</span> firstLevelReduce<span class="token punctuation">;</span>
            <span class="token punctuation">&#125;</span>
        <span class="token punctuation">&#125;</span> <span class="token keyword">else</span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>hasChild<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                after <span class="token operator">=</span> money <span class="token operator">-</span> secondLevelReduce<span class="token punctuation">;</span>
            <span class="token punctuation">&#125;</span>
        <span class="token punctuation">&#125;</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>after <span class="token operator">>=</span> firstLevel<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            tax <span class="token operator">=</span> after <span class="token operator">*</span> <span class="token number">0.03</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>after <span class="token operator">>=</span> secondLevel<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            tax <span class="token operator">=</span> after <span class="token operator">*</span> <span class="token number">0.05</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span>
        <span class="token keyword">return</span> tax<span class="token punctuation">;</span>
 <span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>过程式避免不了if else的嵌套，即便重构基于设计模式的优化，比如策略或者责任链，杀鸡用牛刀不说，扩展性好了，但是可读性差了。<br>看一下使用kotlin的版本</p>
<pre class="line-numbers language-kotlin" data-language="kotlin"><code class="language-kotlin"><span class="token comment">/**
 * 计算个人所得税
 * 如果一个人有房子则减免100再计税
 * 如果一个人有孩子则减免200再计税
 * 减免后大于等于1000则缴税减免后金额的3%
 * 减免后大于等于3000则缴税减免后金额的5%
 * 求应交税多少，不考虑精度丢失等情况
 */</span>
<span class="token keyword">data</span> <span class="token keyword">class</span> <span class="token function">Person</span><span class="token punctuation">(</span><span class="token keyword">val</span> hasHouse<span class="token operator">:</span> Boolean<span class="token punctuation">,</span> <span class="token keyword">val</span> hasChild<span class="token operator">:</span> Boolean<span class="token punctuation">,</span> <span class="token keyword">val</span> money<span class="token operator">:</span> Double<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token keyword">private</span> <span class="token keyword">var</span> actualReduce<span class="token operator">:</span> Double <span class="token operator">=</span> <span class="token keyword">when</span> <span class="token punctuation">(</span><span class="token function">Pair</span><span class="token punctuation">(</span>hasHouse<span class="token punctuation">,</span> hasChild<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token function">Pair</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token operator">-></span> HAS_HOUSE_REDUCE <span class="token operator">+</span> HAS_CHILD_REDUCE
        <span class="token function">Pair</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">)</span> <span class="token operator">-></span> HAS_HOUSE_REDUCE
        <span class="token function">Pair</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token operator">-></span> HAS_CHILD_REDUCE
        <span class="token keyword">else</span> <span class="token operator">-></span> <span class="token number">0.0</span>
    <span class="token punctuation">&#125;</span>

    <span class="token keyword">companion</span> <span class="token keyword">object</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> FIRST_LEVEL <span class="token operator">=</span> <span class="token number">1000.0</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> FIRST_LEVEL_RATE <span class="token operator">=</span> <span class="token number">0.03</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> SECOND_LEVEL <span class="token operator">=</span> <span class="token number">3000.0</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> SECOND_LEVEL_RATE <span class="token operator">=</span> <span class="token number">0.05</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> HAS_HOUSE_REDUCE <span class="token operator">=</span> <span class="token number">100.0</span>
        <span class="token keyword">private</span> <span class="token keyword">const</span> <span class="token keyword">val</span> HAS_CHILD_REDUCE <span class="token operator">=</span> <span class="token number">200.0</span>
    <span class="token punctuation">&#125;</span>

    <span class="token keyword">fun</span> <span class="token function">tax</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">:</span> Double <span class="token punctuation">&#123;</span>
        <span class="token keyword">return</span> <span class="token keyword">when</span> <span class="token punctuation">(</span><span class="token keyword">val</span> after <span class="token operator">=</span> money <span class="token operator">-</span> actualReduce<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">in</span> FIRST_LEVEL<span class="token operator">..</span>SECOND_LEVEL <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
                after <span class="token operator">*</span> FIRST_LEVEL_RATE
            <span class="token punctuation">&#125;</span>
            <span class="token keyword">in</span> SECOND_LEVEL<span class="token operator">..</span>Double<span class="token punctuation">.</span>MAX_VALUE <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
                after <span class="token operator">*</span> SECOND_LEVEL_RATE
            <span class="token punctuation">&#125;</span>
            <span class="token keyword">else</span> <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
                <span class="token number">0.0</span>
            <span class="token punctuation">&#125;</span>
        <span class="token punctuation">&#125;</span>
    <span class="token punctuation">&#125;</span>

<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>虽然有点不公平，因为使用了类，但是其实逻辑都差不多，关键还是使用了when模式匹配，以及after的表达式匹配<br>虽然你说when case不就是switch么，其实不是，因为模式匹配可以匹配类型，表达式等等，而switch只能是值（整数或字符串）。<br>最关键的是可读性提高了，不需要注释说明，即可知道代码所表达的逻辑，接近自然语言。</p>
<h3 id="结束"><a href="#结束" class="headerlink" title="结束"></a>结束</h3><p>当然函数式还有很多没有介绍的，比如Typeclass，函数式的集合，集合的折叠fold,map,flatMap等等，以及函数式范畴学的Monad<br>但是咱只是简介嘛，所以以后有机会再深入介绍吧。</p>

                
            </div>
            <hr/>

            

    <div class="reprint" id="reprint-statement">
        
            <div class="reprint__author">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-user">
                        文章作者:
                    </i>
                </span>
                <span class="reprint-info">
                    <a href="https://dengwu.wang" rel="external nofollow noreferrer">王登武</a>
                </span>
            </div>
            <div class="reprint__type">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-link">
                        文章链接:
                    </i>
                    </span>
                <span class="reprint-info">
                    <a href="https://dengwu.wang/2021/11/24/han-shu-shi-bian-cheng-jian-jie/">https://dengwu.wang/2021/11/24/han-shu-shi-bian-cheng-jian-jie/</a>
                </span>
            </div>
            <div class="reprint__notice">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-copyright">
                        版权声明:
                    </i>
                </span>
                <span class="reprint-info">
                    本博客所有文章除特別声明外，均采用
                    <a href="https://creativecommons.org/licenses/by-nc-nd/4.0/deed.zh" rel="external nofollow noreferrer" target="_blank">CC BY-NC-ND 4.0</a>
                    许可协议。转载请注明来源
                    <a href="https://dengwu.wang" target="_blank">王登武</a>
                    !
                </span>
            </div>
        
    </div>

    <script async defer>
      document.addEventListener("copy", function (e) {
        let toastHTML = '<span>复制成功，请遵循本文的转载规则</span><button class="btn-flat toast-action" onclick="navToReprintStatement()" style="font-size: smaller">查看</a>';
        M.toast({html: toastHTML})
      });

      function navToReprintStatement() {
        $("html, body").animate({scrollTop: $("#reprint-statement").offset().top - 80}, 800);
      }
    </script>



            <div class="tag_share" style="display: block;">
                <div class="post-meta__tag-list" style="display: inline-block;">
                    
                        <div class="article-tag">
                            
                                <a href="/tags/%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BC%96%E7%A8%8B/">
                                    <span class="chip bg-color">函数式编程</span>
                                </a>
                            
                        </div>
                    
                </div>
                <div class="post_share" style="zoom: 80%; width: fit-content; display: inline-block; float: right; margin: -0.15rem 0;">
                    <link rel="stylesheet" type="text/css" href="/libs/share/css/share.min.css">
<div id="article-share">

    
    <div class="social-share" data-sites="qq,qzone,wechat,weibo" data-wechat-qrcode-helper="<p>微信扫一扫即可分享！</p>"></div>
    <script src="/libs/share/js/social-share.min.js"></script>
    

    

</div>

                </div>
            </div>
            
                <style>
    #reward {
        margin: 40px 0;
        text-align: center;
    }

    #reward .reward-link {
        font-size: 1.4rem;
        line-height: 38px;
    }

    #reward .btn-floating:hover {
        box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2), 0 5px 15px rgba(0, 0, 0, 0.2);
    }

    #rewardModal {
        width: 320px;
        height: 350px;
    }

    #rewardModal .reward-title {
        margin: 15px auto;
        padding-bottom: 5px;
    }

    #rewardModal .modal-content {
        padding: 10px;
    }

    #rewardModal .close {
        position: absolute;
        right: 15px;
        top: 15px;
        color: rgba(0, 0, 0, 0.5);
        font-size: 1.3rem;
        line-height: 20px;
        cursor: pointer;
    }

    #rewardModal .close:hover {
        color: #ef5350;
        transform: scale(1.3);
        -moz-transform:scale(1.3);
        -webkit-transform:scale(1.3);
        -o-transform:scale(1.3);
    }

    #rewardModal .reward-tabs {
        margin: 0 auto;
        width: 210px;
    }

    .reward-tabs .tabs {
        height: 38px;
        margin: 10px auto;
        padding-left: 0;
    }

    .reward-content ul {
        padding-left: 0 !important;
    }

    .reward-tabs .tabs .tab {
        height: 38px;
        line-height: 38px;
    }

    .reward-tabs .tab a {
        color: #fff;
        background-color: #ccc;
    }

    .reward-tabs .tab a:hover {
        background-color: #ccc;
        color: #fff;
    }

    .reward-tabs .wechat-tab .active {
        color: #fff !important;
        background-color: #22AB38 !important;
    }

    .reward-tabs .alipay-tab .active {
        color: #fff !important;
        background-color: #019FE8 !important;
    }

    .reward-tabs .reward-img {
        width: 210px;
        height: 210px;
    }
</style>

<div id="reward">
    <a href="#rewardModal" class="reward-link modal-trigger btn-floating btn-medium waves-effect waves-light red">赏</a>

    <!-- Modal Structure -->
    <div id="rewardModal" class="modal">
        <div class="modal-content">
            <a class="close modal-close"><i class="fas fa-times"></i></a>
            <h4 class="reward-title">你的赏识是我前进的动力</h4>
            <div class="reward-content">
                <div class="reward-tabs">
                    <ul class="tabs row">
                        <li class="tab col s6 wechat-tab waves-effect waves-light">
                            <a href="#wechat">微 信</a>
                        </li>
                        <li class="tab col s6 alipay-tab waves-effect waves-light">
                            <a href="#alipay">支付宝</a>
                        </li>
                    </ul>
                    <div id="wechat">
                        <img src="/medias/reward/wechat.jpg" class="reward-img" alt="微信打赏二维码">
                    </div>
                    <div id="alipay">
                        <img src="/medias/reward/alipay1.jpg" class="reward-img" alt="支付宝打赏二维码">
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

<script>
    $(function () {
        $('.tabs').tabs();
    });
</script>

            
        </div>
    </div>

    

    

    

    

    

    

    

    

    <script src="https://utteranc.es/client.js"
        repo="wangdengwu/wangdengwu.github.io"
        issue-term="pathname"
        theme="github-light"
        crossorigin="anonymous"
        async>
    </script>

    

<article id="prenext-posts" class="prev-next articles">
    <div class="row article-row">
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge left-badge text-color">
                <i class="fas fa-chevron-left"></i>&nbsp;上一篇</div>
            <div class="card">
                <a href="/2021/12/01/shen-ru-qian-chu-hikaricp-shu-ju-ku-lian-jie-chi/">
                    <div class="card-image">
                        
                        
                        <img src="/medias/featureimages/0.jpg" class="responsive-img" alt="深入浅出HikariCP数据库连接池">
                        
                        <span class="card-title">深入浅出HikariCP数据库连接池</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            
                        
                    </div>
                    <div class="publish-info">
                        <span class="publish-date">
                            <i class="far fa-clock fa-fw icon-date"></i>2021-12-01
                        </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/categories/Java/" class="post-category">
                                    Java
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/tags/HikariCP/">
                        <span class="chip bg-color">HikariCP</span>
                    </a>
                    
                    <a href="/tags/%E6%95%B0%E6%8D%AE%E5%BA%93%E8%BF%9E%E6%8E%A5%E6%B1%A0/">
                        <span class="chip bg-color">数据库连接池</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge right-badge text-color">
                下一篇&nbsp;<i class="fas fa-chevron-right"></i>
            </div>
            <div class="card">
                <a href="/2021/11/10/echarts5-tu-biao-xuan-ran-guo-cheng-fen-xi/">
                    <div class="card-image">
                        
                        
                        <img src="/medias/featureimages/12.jpg" class="responsive-img" alt="echarts5图表渲染过程分析">
                        
                        <span class="card-title">echarts5图表渲染过程分析</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            
                        
                    </div>
                    <div class="publish-info">
                            <span class="publish-date">
                                <i class="far fa-clock fa-fw icon-date"></i>2021-11-10
                            </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/categories/%E5%89%8D%E7%AB%AF/" class="post-category">
                                    前端
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/tags/%E5%9B%BE%E8%A1%A8-echarts/">
                        <span class="chip bg-color">图表 - echarts</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
    </div>
</article>

</div>


<script>
    $('#articleContent').on('copy', function (e) {
        // IE8 or earlier browser is 'undefined'
        if (typeof window.getSelection === 'undefined') return;

        var selection = window.getSelection();
        // if the selection is short let's not annoy our users.
        if (('' + selection).length < Number.parseInt('120')) {
            return;
        }

        // create a div outside of the visible area and fill it with the selected text.
        var bodyElement = document.getElementsByTagName('body')[0];
        var newdiv = document.createElement('div');
        newdiv.style.position = 'absolute';
        newdiv.style.left = '-99999px';
        bodyElement.appendChild(newdiv);
        newdiv.appendChild(selection.getRangeAt(0).cloneContents());

        // we need a <pre> tag workaround.
        // otherwise the text inside "pre" loses all the line breaks!
        if (selection.getRangeAt(0).commonAncestorContainer.nodeName === 'PRE' || selection.getRangeAt(0).commonAncestorContainer.nodeName === 'CODE') {
            newdiv.innerHTML = "<pre>" + newdiv.innerHTML + "</pre>";
        }

        var url = document.location.href;
        newdiv.innerHTML += '<br />'
            + '来源: 武码公社<br />'
            + '文章作者: 王登武<br />'
            + '文章链接: <a href="' + url + '">' + url + '</a><br />'
            + '本文章著作权归作者所有，任何形式的转载都请注明出处。';

        selection.selectAllChildren(newdiv);
        window.setTimeout(function () {bodyElement.removeChild(newdiv);}, 200);
    });
</script>


<!-- 代码块功能依赖 -->
<script type="text/javascript" src="/libs/codeBlock/codeBlockFuction.js"></script>

<!-- 代码语言 -->

<script type="text/javascript" src="/libs/codeBlock/codeLang.js"></script>


<!-- 代码块复制 -->

<script type="text/javascript" src="/libs/codeBlock/codeCopy.js"></script>


<!-- 代码块收缩 -->

<script type="text/javascript" src="/libs/codeBlock/codeShrink.js"></script>


    </div>
    <div id="toc-aside" class="expanded col l3 hide-on-med-and-down">
        <div class="toc-widget card" style="background-color: white;">
            <div class="toc-title"><i class="far fa-list-alt"></i>&nbsp;&nbsp;目录</div>
            <div id="toc-content"></div>
        </div>
    </div>
</div>

<!-- TOC 悬浮按钮. -->

<div id="floating-toc-btn" class="hide-on-med-and-down">
    <a class="btn-floating btn-large bg-color">
        <i class="fas fa-list-ul"></i>
    </a>
</div>


<script src="/libs/tocbot/tocbot.min.js"></script>
<script>
    $(function () {
        tocbot.init({
            tocSelector: '#toc-content',
            contentSelector: '#articleContent',
            headingsOffset: -($(window).height() * 0.4 - 45),
            collapseDepth: Number('0'),
            headingSelector: 'h2, h3, h4'
        });

        // modify the toc link href to support Chinese.
        let i = 0;
        let tocHeading = 'toc-heading-';
        $('#toc-content a').each(function () {
            $(this).attr('href', '#' + tocHeading + (++i));
        });

        // modify the heading title id to support Chinese.
        i = 0;
        $('#articleContent').children('h2, h3, h4').each(function () {
            $(this).attr('id', tocHeading + (++i));
        });

        // Set scroll toc fixed.
        let tocHeight = parseInt($(window).height() * 0.4 - 64);
        let $tocWidget = $('.toc-widget');
        $(window).scroll(function () {
            let scroll = $(window).scrollTop();
            /* add post toc fixed. */
            if (scroll > tocHeight) {
                $tocWidget.addClass('toc-fixed');
            } else {
                $tocWidget.removeClass('toc-fixed');
            }
        });

        
        /* 修复文章卡片 div 的宽度. */
        let fixPostCardWidth = function (srcId, targetId) {
            let srcDiv = $('#' + srcId);
            if (srcDiv.length === 0) {
                return;
            }

            let w = srcDiv.width();
            if (w >= 450) {
                w = w + 21;
            } else if (w >= 350 && w < 450) {
                w = w + 18;
            } else if (w >= 300 && w < 350) {
                w = w + 16;
            } else {
                w = w + 14;
            }
            $('#' + targetId).width(w);
        };

        // 切换TOC目录展开收缩的相关操作.
        const expandedClass = 'expanded';
        let $tocAside = $('#toc-aside');
        let $mainContent = $('#main-content');
        $('#floating-toc-btn .btn-floating').click(function () {
            if ($tocAside.hasClass(expandedClass)) {
                $tocAside.removeClass(expandedClass).hide();
                $mainContent.removeClass('l9');
            } else {
                $tocAside.addClass(expandedClass).show();
                $mainContent.addClass('l9');
            }
            fixPostCardWidth('artDetail', 'prenext-posts');
        });
        
    });
</script>

    

</main>




    <footer class="page-footer bg-color">
    

    <div class="container row center-align"
         style="margin-bottom: 0px !important;">
        <div class="col s12 m8 l8 copy-right">
            Copyright&nbsp;&copy;
            
                <span id="year">2021-2022</span>
            
            <!-- <a href="/about" target="_blank">王登武</a>
            |&nbsp;Powered by&nbsp;<a href="https://hexo.io/" target="_blank">Hexo</a>
            |&nbsp;Theme&nbsp;<a href="https://github.com/blinkfox/hexo-theme-matery" target="_blank">Matery</a> -->
            <!-- <br> -->
            
                &nbsp;<i class="fas fa-chart-area"></i>&nbsp;站点总字数:&nbsp;<span
                        class="white-color">31.6k</span>
            
            
            
            
            
            <!-- <br> -->

            <!-- 运行天数提醒. -->
            
            <br>
            
                <span id="icp"><img src="/medias/icp.png"
                                    style="vertical-align: text-bottom;"/>
                <a href="https://beian.miit.gov.cn/" target="_blank">陕ICP备2021012627号-2</a>
            </span>
            
        </div>
        <div class="col s12 m4 l4 social-link ">
    <a href="https://github.com/wangdengwu" class="tooltipped" target="_blank" data-tooltip="访问我的GitHub" data-position="top" data-delay="50">
        <i class="fab fa-github"></i>
    </a>



    <a href="mailto:me@dengwu.wang" class="tooltipped" target="_blank" data-tooltip="邮件联系我" data-position="top" data-delay="50">
        <i class="fas fa-envelope-open"></i>
    </a>







    <a href="tencent://AddContact/?fromId=50&fromSubId=1&subcmd=all&uin=251472795" class="tooltipped" target="_blank" data-tooltip="QQ联系我: 251472795" data-position="top" data-delay="50">
        <i class="fab fa-qq"></i>
    </a>





    <a href="https://www.zhihu.com/people/wangdengwu" class="tooltipped" target="_blank" data-tooltip="关注我的知乎: https://www.zhihu.com/people/wangdengwu" data-position="top" data-delay="50">
        <i class="fab fa-zhihu1">知</i>
    </a>



</div>
    </div>
</footer>

<div class="progress-bar"></div>


    <!-- 搜索遮罩框 -->
<div id="searchModal" class="modal">
    <div class="modal-content">
        <div class="search-header">
            <span class="title"><i class="fas fa-search"></i>&nbsp;&nbsp;搜索</span>
            <input type="search" id="searchInput" name="s" placeholder="请输入搜索的关键字"
                   class="search-input">
        </div>
        <div id="searchResult"></div>
    </div>
</div>

<script type="text/javascript">
$(function () {
    var searchFunc = function (path, search_id, content_id) {
        'use strict';
        $.ajax({
            url: path,
            dataType: "xml",
            success: function (xmlResponse) {
                // get the contents from search data
                var datas = $("entry", xmlResponse).map(function () {
                    return {
                        title: $("title", this).text(),
                        content: $("content", this).text(),
                        url: $("url", this).text()
                    };
                }).get();
                var $input = document.getElementById(search_id);
                var $resultContent = document.getElementById(content_id);
                $input.addEventListener('input', function () {
                    var str = '<ul class=\"search-result-list\">';
                    var keywords = this.value.trim().toLowerCase().split(/[\s\-]+/);
                    $resultContent.innerHTML = "";
                    if (this.value.trim().length <= 0) {
                        return;
                    }
                    // perform local searching
                    datas.forEach(function (data) {
                        var isMatch = true;
                        var data_title = data.title.trim().toLowerCase();
                        var data_content = data.content.trim().replace(/<[^>]+>/g, "").toLowerCase();
                        var data_url = data.url;
                        data_url = data_url.indexOf('/') === 0 ? data.url : '/' + data_url;
                        var index_title = -1;
                        var index_content = -1;
                        var first_occur = -1;
                        // only match artiles with not empty titles and contents
                        if (data_title !== '' && data_content !== '') {
                            keywords.forEach(function (keyword, i) {
                                index_title = data_title.indexOf(keyword);
                                index_content = data_content.indexOf(keyword);
                                if (index_title < 0 && index_content < 0) {
                                    isMatch = false;
                                } else {
                                    if (index_content < 0) {
                                        index_content = 0;
                                    }
                                    if (i === 0) {
                                        first_occur = index_content;
                                    }
                                }
                            });
                        }
                        // show search results
                        if (isMatch) {
                            str += "<li><a href='" + data_url + "' class='search-result-title'>" + data_title + "</a>";
                            var content = data.content.trim().replace(/<[^>]+>/g, "");
                            if (first_occur >= 0) {
                                // cut out 100 characters
                                var start = first_occur - 20;
                                var end = first_occur + 80;
                                if (start < 0) {
                                    start = 0;
                                }
                                if (start === 0) {
                                    end = 100;
                                }
                                if (end > content.length) {
                                    end = content.length;
                                }
                                var match_content = content.substr(start, end);
                                // highlight all keywords
                                keywords.forEach(function (keyword) {
                                    var regS = new RegExp(keyword, "gi");
                                    match_content = match_content.replace(regS, "<em class=\"search-keyword\">" + keyword + "</em>");
                                });

                                str += "<p class=\"search-result\">" + match_content + "...</p>"
                            }
                            str += "</li>";
                        }
                    });
                    str += "</ul>";
                    $resultContent.innerHTML = str;
                });
            }
        });
    };

    searchFunc('/search.xml', 'searchInput', 'searchResult');
});
</script>

    <!-- 回到顶部按钮 -->
<div id="backTop" class="top-scroll">
    <a class="btn-floating btn-large waves-effect waves-light" href="#!">
        <i class="fas fa-arrow-up"></i>
    </a>
</div>


    <script src="/libs/materialize/materialize.min.js"></script>
    <script src="/libs/masonry/masonry.pkgd.min.js"></script>
    <script src="/libs/aos/aos.js"></script>
    <script src="/libs/scrollprogress/scrollProgress.min.js"></script>
    <script src="/libs/lightGallery/js/lightgallery-all.min.js"></script>
    <script src="/js/matery.js"></script>

    

    <!-- 雪花特效 -->
    

    <!-- 鼠标星星特效 -->
    

    <!-- Baidu Analytics -->

    <!-- Baidu Push -->

<script>
    (function () {
        var bp = document.createElement('script');
        var curProtocol = window.location.protocol.split(':')[0];
        if (curProtocol === 'https') {
            bp.src = 'https://zz.bdstatic.com/linksubmit/push.js';
        } else {
            bp.src = 'http://push.zhanzhang.baidu.com/push.js';
        }
        var s = document.getElementsByTagName("script")[0];
        s.parentNode.insertBefore(bp, s);
    })();
</script>

    
    <script src="/libs/others/clicklove.js" async="async"></script>
    
    

    

    

    <!--腾讯兔小巢-->
    
    

    

    

    
    <script src="/libs/instantpage/instantpage.js" type="module"></script>
    

</body>

</html>
